fix(01-01): build Docker image from repo-root pnpm workspace context

The walking-skeleton Dockerfile built from a ./apps/api context and could not
work in a pnpm workspace: the lockfile lives at the repo root, pnpm 11 refused
esbuild's build script without the root pnpm-workspace.yaml, the dev stage never
compiled src->dist, and the production stage had invalid COPY syntax referencing
a path outside its context.

Switch to the correct monorepo pattern: build from the repo-root context, copy
the workspace manifest + lockfile + both package.jsons, and install with
--frozen-lockfile --filter @familysync/api...  Reorder stages so production is
default; dev reuses builder output. Fix the dev volume mount path.

Surfaced while clearing the Task 3 checkpoint (stack bring-up): drizzle-kit push
applied the 4 tables and /health returned {ok:true,db:up} end-to-end.

docker-compose.dev.yml

@@ -2,10 +2,11 @@
 services:
   api:
     build:
-      context: ./apps/api
+      context: .
+      dockerfile: apps/api/Dockerfile
       target: dev
     volumes:
-      - ./apps/api/src:/app/src
+      - ./apps/api/src:/app/apps/api/src
     environment:
       NODE_ENV: development